Abstract:

A method for forming an insulating film includes forming a silicon nitride
film on a silicon surface by subjecting a target substrate wherein
silicon is exposed in the surface to a treatment for nitriding the
silicon, forming a silicon oxynitride film by heating the target
substrate provided with the silicon nitride film in an N2O
atmosphere, and nitriding the silicon oxynitride film.

Claims:

1. A method for forming an insulating film comprising:forming a silicon
nitride film by performing a silicon nitriding on a silicon surface
formed on a target substrate by using a plasma mainly including radicals;
andforming a silicon oxynitride film by performing a heat treatment on
the target substrate provided with the silicon nitride film in an
N2O atmosphere,wherein the silicon nitriding is performed by using a
plasma of a rare gas and a nitrogen containing gas, and the heat
treatment is performed at a processing pressure ranging from 133.3 to
1333 Pa and a processing temperature ranging from 900 to 1200.degree. C.

2. (canceled)

3. The method of claim 1, wherein the silicon nitriding is performed by
using a nitrogen containing plasma formed by introducing microwaves into
a processing chamber by a planar antenna having a plurality of slots.

4. The method of claim 1, wherein a film thickness of the silicon nitride
film formed by the silicon nitriding ranges from 0.5 to 1 nm.

5. The method of claim 1, wherein the heat treatment in an N2O
atmosphere is performed in a mixed atmosphere of N2O and N2, or
in an N2O gas atmosphere.

6-8. (canceled)

9. The method of claim 1, wherein the processing temperature in the heat
treatment in an N2O atmosphere is in a range from 1000 to
1200.degree. C.

10. A method for forming an insulating film comprising:forming a silicon
nitride film by performing a silicon nitriding on a silicon surface
formed on a target substrate by using a plasma mainly including radicals
on a target substrate wherein silicon is exposed in the surface;forming a
silicon oxynitride film by performing a heat treatment on the target
substrate provided with the silicon nitride film in an N2O
atmosphere; andperforming a nitriding of the silicon oxynitride film by
using a plasma mainly including ions,wherein the silicon nitriding and
the nitriding of the silicon oxynitride film are performed by using a
plasma of a rare gas and a nitrogen containing gas, and the heat
treatment is performed at a processing pressure ranging from 133.3 to
1333 Pa and a processing temperature ranging from 900 to 1200.degree. C.

11. (canceled)

12. The method of claim 10, wherein the silicon nitriding is performed by
using a nitrogen containing plasma formed by introducing microwaves into
a processing chamber by a planar antenna having a plurality of slots.

13-15. (canceled)

16. The method for forming an insulating film of claim 10, wherein a film
thickness of the silicon nitride film formed by the silicon nitriding
ranges from 0.5 to 1 nm.

17. The method of claim 10, wherein the heat treatment in an N2O
atmosphere is performed in a mixed atmosphere of N2O and N2, or
in an N2O gas atmosphere.

18-20. (canceled)

21. The method for forming an insulating film of claim 10, wherein the
processing temperature in the heat treatment in an N2O atmosphere is
in a range from 1000 to 1200.degree. C.

22. A method for forming an insulating film comprising:forming a silicon
nitride film by performing a silicon nitriding on a silicon surface
formed on a target substrate by using a plasma mainly including
radicals;forming a silicon oxynitride film by performing a first heat
treatment on the target substrate provided with the silicon nitride film
in an N2O atmosphere;performing a nitriding of the silicon
oxynitride film by using a plasma mainly including ions; andperforming a
second heat treatment on the target substrate after performing the
nitriding of the silicon oxynitride film,wherein the silicon nitriding
and the nitriding of the silicon oxynitride film are performed by using a
plasma of a rare gas and a nitrogen containing gas, the first heat
treatment is performed at a processing pressure ranging from 133.3 to
1333 Pa and a processing temperature ranging from 900 to 1200.degree. C.
and the second heat treatment is performed at a processing pressure
ranging from 133.3 to 1333 Pa and a processing temperature ranging from
800 to 1200.degree. C.

23. (canceled)

24. The method for forming an insulating film of claim 22, wherein the
silicon nitriding is performed by using a nitrogen containing plasma
formed by introducing microwaves into a processing chamber by a planar
antenna having a plurality of slots.

25-27. (canceled)

28. (canceled)

29. The method of claim 22, wherein the first heat treatment is performed
in a mixed atmosphere of N2O and N2, or in an N2O gas only
atmosphere.

30-32. (canceled)

33. The method of claim 22, wherein the processing temperature in the
first heat treatment is in a range from 1000 to 1200.degree. C.

34. The method of claim 22, wherein the second heat treatment is performed
in an N2 gas atmosphere, an O2 gas atmosphere, or in a mixed
atmosphere of N2 and O.sub.2.

35. The method of claim 34, wherein in the second heat treatment, a flow
rate ratio of O2/N2 is in a range from 0 to 0.01.

36-37. (canceled)

38. A method for manufacturing a semiconductor device comprising:forming a
gate insulating film on a silicon substrate; andforming a gate electrode
on the gate insulating film,wherein the gate insulating film is formed by
a method including:forming a silicon nitride film by performing a silicon
nitriding on a silicon surface formed on a target substrate by using a
plasma mainly including radicals; andforming a silicon oxynitride film by
performing a heat treatment on the target substrate provided with the
silicon nitride film in an N2O atmosphere,wherein the heat treatment
is performed at a processing pressure ranging from 133.3 to 1333 Pa and a
processing temperature ranging from 900 to 1200.degree. C.

39. A method for manufacturing a semiconductor device comprising:forming a
gate insulating film on a silicon substrate; andforming a gate electrode
on the gate insulating film,wherein the gate insulating film is formed by
a method including:forming a silicon nitride film by performing a silicon
nitriding on a silicon surface formed on a target substrate by using a
plasma mainly including radicals;forming a silicon oxynitride film by
performing a heat treatment on the target substrate provided with the
silicon nitride film in an N2O atmosphere; andperforming a nitriding
of the silicon oxynitride film by using a plasma mainly including
ions,wherein the heat treatment is performed at a processing pressure
ranging from 133.3 to 1333 Pa and a processing temperature ranging from
900 to 1200.degree. C.

40. A method for manufacturing a semiconductor device comprising:forming a
gate insulating film on a silicon substrate; andforming a gate electrode
on the gate insulating film,wherein the gate insulating film is formed by
a method including:forming a silicon nitride film by performing a silicon
nitriding on a silicon surface formed on a target substrate by using a
plasma mainly including radicals;forming a silicon oxynitride film by
performing a first heat treatment on the target substrate provided with
the silicon nitride film in an N2O atmosphere;performing a nitriding
of the silicon oxynitride film by using a plasma mainly including ions;
andperforming a second heat treatment on the target substrate after
performing the nitriding of the silicon oxynitride film,wherein the first
heat treatment is performed at a processing pressure ranging from 133.3
to 1333 Pa and a processing temperature ranging from 900 to 1200.degree.
C. and the second heat treatment is performed at a processing pressure
ranging from 133.3 to 1333 Pa and a processing temperature ranging from
800 to 1200.degree. C.

41-43. (canceled)

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to a method for forming an insulating
film by performing nitriding and oxidation on a target substrate to be
processed such as a semiconductor substrate or the like and a method for
manufacturing a semiconductor device.

BACKGROUND OF THE INVENTION

[0002]In a manufacturing process of various semiconductor devices, a
silicon nitride film is formed, as a gate insulating film of a
transistor, on a semiconductor substrate. As for a method for forming a
silicon nitride film, in addition to a method for depositing a silicon
oxide film by CVD (Chemical Vapor Deposition), there is suggested a
method for forming a silicon oxynitride film by introducing nitrogen into
a silicon oxide film by plasma processing (e.g., Japanese Patent
Laid-open Publication No. 2001-274148).

[0003]Further, as semiconductor devices are miniaturized, a gate
insulating film becomes thinner, and it is required to form a gate
insulating film having a film thickness of a few nm. Therefore, there is
examined a possibility to form a silicon nitride film by nitriding
silicon directly.

[0004]As for a method for forming a gate insulating film by introducing
nitrogen into a silicon substrate directly, there is suggested a method
for forming an insulating film including: a nitride film forming step of
forming a first nitride film on a semiconductor substrate; an oxide layer
forming step of forming a first oxide layer between the semiconductor
substrate and the nitride film and also forming a second oxide layer on
the nitride film; and an oxide layer nitriding step of forming a second
nitride film or an oxynitride film on the first nitride film by nitriding
the second oxide film (e.g., Japanese Patent Laid-open Publication No.
2005-93865 (JP2005-93865A)). This method has a purpose of obtaining a
uniform film thickness of the formed gate insulating film and reducing an
equivalent oxide thickness (EOT).

[0005]In the method disclosed in JP2005-93865A, the silicon nitride film
is formed by nitriding the silicon substrate directly. Then, the silicon
oxide film, the first silicon nitride film and the second silicon nitride
film (or silicon oxynitride film) are formed on the interface of the
silicon substrate by performing oxidation and nitriding. However, the
gate insulating film formed by this method is disadvantageous in that
interface states and fixed charges thereof change a threshold voltage and
increase a flat band voltage (Vfb), thereby adversely affecting the
mobility of electrons and holes in a transistor. That is, in the
technique disclosed in JP2005-93865A, it is difficult to form a
high-quality gate insulating film which ensures good electrical
characteristics of a transistor.

SUMMARY OF THE INVENTION

[0006]In view of the above, the present invention provides an insulating
film forming method capable of forming a high-quality thin insulating
film by nitriding silicon directly and ensuring good electrical
characteristics.

[0007]Further, the present invention provides a method for manufacturing a
semiconductor device including the above-described insulating film as a
gate insulating film.

[0008]In accordance with a first aspect of the present invention, there is
provided a method for forming an insulating film including: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; and forming a silicon oxynitride film by performing a heat
treatment on the target substrate provided with the silicon nitride film
in an N2O atmosphere.

[0009]In accordance with a second aspect of the present invention, there
is provided a method for forming an insulating film including: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; forming a silicon oxynitride film by performing a heat treatment
on the target substrate provided with the silicon nitride film in an
N2O atmosphere; and performing a nitriding of the silicon oxynitride
film.

[0010]In accordance with a third aspect of the present invention, there is
provided a method for forming an insulating film including: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; forming a silicon oxynitride film by performing a heat treatment
on the target substrate provided with the silicon nitride film in an
N2O atmosphere; performing a nitriding of the silicon oxynitride
film; and performing a heat treatment on the target substrate after
performing the nitriding of the silicon oxynitride film.

[0011]In accordance with the first to third aspects of the present
invention, the silicon nitriding is preferably performed by using a
plasma of a rare gas and a nitrogen containing gas. Further, preferably,
the silicon nitriding is performed by using a nitrogen containing plasma
formed by introducing microwaves into a processing chamber by a planar
antenna having a plurality of slots. In this case, the silicon nitriding
is preferably performed by installing a dielectric plate having a
plurality of through holes between the target substrate provided in the
processing chamber and a plasma generation region. Further, a film
thickness of the silicon nitride film formed by the silicon nitriding
preferably ranges from 0.5 to 2 nm.

[0012]Further, in accordance with the first to third aspects of the
present invention, the heat treatment in an N2O atmosphere is
preferably performed in a mixed atmosphere of N2O and N2, or in
an N2O gas atmosphere. In this case, preferably a flow rate of
N2O is in a range from 50 to 6000 mL/min (sccm), and a flow rate of
N2 is in a range from 0 to 3000 mL/min (sccm). Further, a processing
pressure is preferably in a range from 133.3 to 1333 Pa. Further, a
processing temperature is preferably in a range from 900 to 1200°
C. and, more preferably, in a range from 1000 to 1200° C.

[0013]In accordance with the third aspect of the present invention, the
heat treatment after the nitriding of the silicon oxynitride film is
preferably performed in an N2 gas atmosphere, an O2 gas
atmosphere, or in a mixed atmosphere of N2 and O2. In this
case, a flow rate ratio of O2/N2 is preferably in a range from
0 to 0.01. Further, a processing pressure is preferably in a range from
133.3 to 1333 Pa. Further, a processing temperature is preferably in a
range from 800 to 1200° C.

[0014]In accordance with a fourth aspect of the present invention, there
is provided a method for manufacturing a semiconductor device including:
forming a gate insulating film on a silicon substrate; and forming a gate
electrode on the gate insulating film.

[0015]The gate insulating film is formed by a method includes: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; and forming a silicon oxynitride film by performing a heat
treatment on the target substrate provided with the silicon nitride film
in an N2O atmosphere.

[0016]In accordance with a fifth aspect of the present invention, there is
provided a method for manufacturing a semiconductor device including:
forming a gate insulating film on a silicon substrate; and forming a gate
electrode on the gate insulating film,

[0017]The gate insulating film is formed by a method includes: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; forming a silicon oxynitride film by performing a heat treatment
on the target substrate provided with the silicon nitride film in an
N2O atmosphere; and performing a nitriding of the silicon oxynitride
film.

[0018]In accordance with a sixth aspect of the present invention, there is
provided a method for manufacturing a semiconductor device including:
forming a gate insulating film on a silicon substrate; and forming a gate
electrode on the gate insulating film.

[0019]The gate insulating film is formed by a method includes: forming a
silicon nitride film on a silicon surface by performing a silicon
nitriding on a target substrate wherein silicon is exposed in the
surface; forming a silicon oxynitride film by performing a heat treatment
on the target substrate provided with the silicon nitride film in an
N2O atmosphere; performing a nitriding of the silicon oxynitride
film; and performing a heat treatment on the target substrate after
performing the nitriding of the silicon oxynitride film.

[0020]In accordance with a seventh aspect of the present invention, there
is provided a computer-readable storage medium storing a program for
controlling a substrate processing system including a nitriding
processing apparatus and a heat treatment apparatus. The program, when
executed, controls the substrate processing system in a computer to
execute an insulating film forming method including: forming a silicon
nitride film on a silicon surface by performing a silicon nitriding on a
target substrate wherein silicon is exposed in the surface; and forming a
silicon oxynitride film by performing a heat treatment on the target
substrate provided with the silicon nitride film in an N2O
atmosphere.

[0021]In accordance with a eighth aspect of the present invention, there
is provided a computer-readable storage medium storing a program for
controlling a substrate processing system including a nitriding
processing apparatus and a heat treatment apparatus. The program, when
executed, controls the substrate processing system in a computer to
execute an insulating film forming method includes: forming a silicon
nitride film on a silicon surface by performing a silicon nitriding on a
target substrate wherein silicon is exposed in the surface; forming a
silicon oxynitride film by performing a heat treatment on the target
substrate provided with the silicon nitride film in an N2O
atmosphere; and performing a nitriding of the silicon oxynitride film.

[0022]In accordance with a nine aspect of the present invention, there is
provided a computer-readable storage medium storing a program for
controlling a substrate processing system including a nitriding
processing apparatus and a heat treatment apparatus. The program, when
executed, controls the substrate processing system in a computer to
execute an insulating film forming method includes: forming a silicon
nitride film on a silicon surface by performing a silicon nitriding on a
target substrate wherein silicon is exposed in the surface; forming a
silicon oxynitride film by performing a heat treatment on the target
substrate provided with the silicon nitride film in an N2O
atmosphere; performing a nitriding of the silicon oxynitride film; and
performing a heat treatment on the target substrate after performing the
nitriding of the silicon oxynitride film.

[0023]In accordance with the present invention, a silicon oxynitride film
is formed by performing thermal oxidation on a silicon nitride film
obtained by nitriding a silicon substrate directly, resulting in an
insulating film having a nitrogen and oxygen concentration gradient in a
film depth direction. This insulating film has small amount of fixed
charges in the film and can suppress the flat band voltage Vfb.
Therefore, when this insulating film is used as, e.g., a gate insulating
film of a transistor, good electrical characteristics are ensured. The
method of the present invention which can form a gate insulating film is
suitable for forming a thin gate insulating film of less than about 2 nm
(preferably, from about 0.5 to 1 nm) or the like in manufacturing
semiconductor device such as a transistor or the like which is required
to be miniaturized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a flow chart showing an example of a manufacturing process
of an insulating film of the present invention.

[0025]FIG. 2 provides process cross sectional views illustrating states in
a vicinity of a substrate surface which correspond to respective steps
shown in FIG. 1.

[0026]FIGS. 3A to 3D depict nitrogen and oxygen profiles in an insulating
film which correspond to the respective steps shown in FIG. 1.

[0027]FIG. 4 is a schematic view describing a substrate processing system
that can be used to form an insulating film of the present invention.

[0028]FIG. 5 presents a schematic cross sectional view of a plasma
processing apparatus in the substrate processing system shown in FIG. 4.

[0029]FIG. 6 represents a top view of a plate of the plasma processing
apparatus shown in FIG. 5.

[0030]FIG. 7 describes a cross sectional view of principal parts of the
plate of the plasma processing apparatus shown in FIG. 5.

[0031]FIG. 8 is a top view of a planar antenna member of the plasma
processing apparatus shown in FIG. 5.

[0032]FIG. 9 illustrates a schematic cross sectional view of a heat
treatment apparatus in the processing system shown in FIG. 4.

[0033]FIG. 10A provides a process cross sectional view showing a
manufacturing process of a transistor to which an insulating film forming
method of the present invention is applied, and illustrates a state in
which a device isolation layer is formed.

[0034]FIG. 10B presents a process cross sectional view showing a
manufacturing process of a transistor to which an insulating film forming
method of the present invention is applied, and depicts a state in which
an insulating film is formed.

[0035]FIG. 10C represents a process cross sectional view showing a
manufacturing process of a transistor to which an insulating film forming
method of the present invention is applied, and describes a state in
which a transistor is formed.

[0036]FIG. 11A is a graph showing an XPS analysis result of measuring
in-film oxygen concentration in the case of forming a silicon oxynitride
film by heating a wafer having a silicon nitride film in an N2O
atmosphere.

[0037]FIG. 11B is a graph showing an XPS analysis result of measuring
in-film nitrogen concentration in the case of forming a silicon
oxynitride film by heating a wafer having a silicon nitride film in an
N2O atmosphere.

[0038]FIG. 12 illustrates a graph depicting a relationship between EOT and
Gmmax of a transistor.

[0039]FIG. 13 provides a graph describing a relationship between
Gmmax and a temperature of a thermal oxidation process.

[0040]FIG. 14 presents a graph showing a relationship between Jg and a
temperature in a thermal oxidation process.

[0041]FIG. 15 represents a graph illustrating a relationship among a
processing pressure, a film thickness of a silicon oxynitride film, and
nitrogen concentration in the film.

[0042]FIG. 16A offers a graph showing a nitrogen atom concentration
profile in a film depth direction in accordance with silicon oxynitride
film forming conditions.

[0043]FIG. 16B is a graph showing an oxygen atom concentration profile in
a film depth direction in accordance with silicon oxynitride film forming
conditions.

[0044]FIG. 16C sets forth a graph showing a silicon atom concentration
profile in a film depth direction in accordance with silicon oxynitride
film forming conditions.

[0045]FIG. 17 provides a graph showing Gmmax in various tests.

[0046]FIG. 18 depicts a graph illustrating Jg in various tests.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047]The embodiments of the present invention will be described with
reference to the accompanying drawings.

[0048]FIG. 1 is a flow chart showing exemplary steps of an insulating film
forming method of the present invention. Here, there will be described,
as an example, formation of an insulating film that can be used as a gate
insulating film of a transistor. Further, FIG. 2 schematically
illustrates states of a semiconductor wafer surface which correspond to
respective steps S1 to S4 shown in FIG. 1. FIGS. 3A to 3D depict nitrogen
and oxygen profiles in a depth direction of an insulating film which are
measured after the completion of the above steps.

[0049]First of all, in a step S1, a nitriding process is performed on a
silicon substrate 301 such as a semiconductor wafer W (hereinafter,
referred to as a "wafer") or the like (first nitriding process). By
performing the first nitriding process, a silicon nitride film (SiN film)
303 is formed on a silicon layer 302 of the silicon substrate 301. The
nitriding process in the step S1 can be performed by various methods,
e.g., heating, plasma processing and the like, without being limited to a
specific method. However, in order to form a thin silicon nitride film of
a thickness less than about 1 nm, it is preferable to perform a plasma
nitriding process by using, e.g., a plasma processing apparatus 100 (to
be described later) shown in FIG. 5 capable of performing a
low-temperature processing at a low electron temperature of about 0.5 to
1 eV with a high-density plasma.

[0050]When the plasma nitriding process is performed by using the plasma
processing apparatus, a flow rate of a rare gas, e.g., Ar or the like, is
set to be in a range from about 100 to 6000 mL/min (sccm), and a flow
rate of N2 gas is set to be in a range from about 10 to 2000 mL/min
(sccm). In this case, a flow rate ratio of Ar and N2, i.e.,
Ar/N2, is set to be in a range from about 0.5 to 600, and preferably
in a range from about 2 to 200. Further, a processing pressure level in a
chamber is controlled to be in a range from about 66.7 to 1333 Pa (in a
range from about 0.05 to 10 Torr), preferably in a range from about 200
to 667 Pa (in a range from about 1.5 to 5 Torr), and more preferably
about 200 to 266.6 Pa (in the range from about 1.5 to 2 Torr). The wafer
W is heated to a temperature in a range from about 300 to 800° C.,
preferably in a range from about 400 to 800° C., and more
preferably in a range from about 600 to 800° C. Moreover, a
microwave power is preferably set to be in a range from about 500 to 2000
W. When a plate 60 (to be described later) is not provided, the
processing pressure level is preferably controlled to be in a range from
about 133.3 to 1333 Pa (in a range about 1 to 10 Torr). That is, in the
first nitriding process of the step S1, it is preferable to perform the
nitriding process under the conditions in which a plasma mainly including
radicals is generated.

[0051]The silicon nitride film 303 obtained after the completion of the
step S1 is a high-quality insulating film having a small gate leakage
current Jg despite that a physical film thickness thereof is about 1 nm.
In that state, however, fixed charges are generated at the interface
between the silicon nitride film 303 and the silicon layer 302, as can be
seen from FIG. 3A. Accordingly, the mobility of a carrier deteriorates,
and a threshold voltage Vth of a transistor is shifted, which makes it
difficult to obtain a high Gm (trans-conductance) or high on current
(Ion) characteristics. The Gm and the ion characteristics greatly affect
reliability of a device as a gate insulating film.

[0052]Next, in a step S2, the silicon substrate 301 on which the silicon
nitride film 303 is formed is oxidized by using, e.g., a heat treatment
apparatus 101 (to be described later) shown in FIG. 9 (thermal oxidation;
first annealing). As a consequence, oxygen is introduced into the silicon
nitride film 303, forming a silicon oxynitride film (SiON film) 304
having an oxygen concentration gradient decreasing from the surface side
toward the interface with the silicon layer 302. In this oxidation
process, an N2O gas or a gaseous mixture of N2O gas and N2
gas is used. Preferably, a flow rate of N2O is in a range from about
50 to 6000 mL/min (sccm), and a flow rate of N2 is in a range from
about 0 to 6000 mL/min (sccm). At this time, an N2O partial pressure
is preferably higher than or equal to about 3.3 Pa and lower than or
equal to about 133.3 Pa. Further, the heat treatment is preferably
performed for about 0.1 to 2 minutes at a processing pressure controlled
to be in a range from about 133.3 to 1333 Pa and a processing temperature
ranging from about 900 to 1200° C. It is preferable that the
processing pressure is higher. Preferably, it is higher than or equal to
about 1000° C. and, more preferably, it is in a range from about
1000 to 1200° C.

[0053]As illustrated in FIG. 3B, the silicon oxynitride film 304 formed by
performing thermal oxidation at a high temperature ranging from about
1000 to 1200° C. in an N2O gas atmosphere has a nitrogen
concentration profile which is low at the surface side and increases
toward the interface with the silicon layer 302 in a depth direction but
decreases at the interface. Meanwhile, the oxygen concentration has an
overall tendency to decrease from the surface side of the silicon
oxynitride film 304 toward the interface of the silicon layer 302, but
shows a profile in which oxygen is introduced into the interface at a
specific level of concentration. Since Si--O is formed at the interface
between the silicon layer 302 and the silicon oxynitride film 304 having
such nitrogen/oxygen concentration profile, the fixed charges in the
insulating film can be reduced.

[0054]That is, by converting Si--SiN bonds into Si--SiO bonds, it is
possible to reduce the interface states and the flat band voltage Vfb. In
addition, the shift of the threshold voltage Vth of the transistor is
improved, and high Gm or ion characteristics are obtained. Accordingly,
the device characteristics are improved.

[0055]By performing the first nitriding process of the step S1 and the
oxidation process of the step S2, it is possible to form an insulating
film of a high Gm, reduced leakage current and Vfb, thereby obtaining
good electrical characteristics. In addition to the processes of the
steps S1 and S2, a second nitriding process of a step S3 may be
performed, which makes it possible to further reduce the leakage current
and Vfb. Further, in addition to the processes of the steps S1 to S3, an
annealing process of a step S4 may be carried out. By performing the
processes of the steps S1 to S3 or the processes of the steps S1 to S4,
it is possible to form an insulating film having better electrical
characteristics and obtain good device characteristics.

[0056]In the step S3, only a surface side of the silicon oxynitride film
(SiON film) 304 is subjected to a plasma nitriding process by using, as a
plasma processing apparatus, e.g., the plasma processing apparatus 100
(to be described later) shown in FIG. 5 (second nitriding process). By
performing the nitriding process of the step S3, nitrogen is newly
introduced into the surface side of the silicon oxynitride film 304
(e.g., up to about 0.5 nm in a depth direction) and, thus, the silicon
oxynitride film 305 having an increased nitrogen concentration at a
surface layer compared to that measured after the completion of the step
S2 (see FIG. 3B) is formed, as shown in FIG. 3C. By increasing the
nitrogen concentration at the surface side, it is possible to prevent a
leakage current and penetration of boron while maintaining an effect of
suppressing a shift of a threshold voltage Vth of a transistor and a high
Gm and high ion characteristics. As a consequence, the reliability of the
semiconductor devices can be improved.

[0057]When the substrate surface is nitrided by the plasma processing
apparatus, a flow rate of rare gas, e.g., Ar or the like, is set to be in
the range from about 100 to 6000 mL/min (sccm), and a flow rate of
N2 gas is set to be in the range from about 5 to 2000 mL/min (sccm).
In this case, a flow rate ratio of Ar and N2, i.e., Ar/N2,
ranges from about 0.5 to 600, and preferably from about 2 to 200.
Further, a processing pressure level in a chamber is controlled to be in
the range from about 0.66 to 1333 Pa (5 mTorr to 10 Torr), preferably in
the range from about 1.33 to 26.6 Pa (5 mTorr to 0.2 Torr), and more
preferably in the range from about 1.33 to 12 Pa (5 to 90 mTorr). A
temperature of the wafer W is heated to be in the range from about 200 to
600° C., preferably in the range from about 200 to 400° C.,
and more preferably in the range from about 300 to 400° C.
Besides, a microwave power is preferably in the range from about 500 to
2000 W.

[0058]When the plate 60 is not provided, it is preferable that the
processing pressure level is controlled to be in the range from about 6.6
to 26.6 Pa (in the range from about 0.05 to 0.2 Torr).

[0059]As described above, in the second nitriding process of the step S3,
the nitriding process is preferably performed by generating a plasma
mainly including ions. This plasma preferably has an electron temperature
in a range from about 0.5 to 2 eV and a high density ranging from about
1×1010 to 5×1012/cm3.

[0060]By performing the processes of the steps S1 to S3, on the silicon
layer 302 of the silicon substrate 301, nitrogen of a certain level is
introduced near the surface toward the interface with the silicon layer
302, thus forming the silicon oxynitride film 305 having a profile of
nitrogen concentration decreasing in a depth direction at the interface.

[0061]Thereafter, in the step S4, annealing is performed to improve
insulation characteristics by densifying the silicon oxynitride film 305.
The annealing can be carried out by using, e.g., the heat treatment
apparatus 101 shown in FIG. 9. At this time, the annealing can be
performed in an N2 gas atmosphere, an N2O gas atmosphere, an
O2 gas atmosphere or a mixed atmosphere of these gases, and
preferably in an N2 gas atmosphere, an O2 gas atmosphere or a
mixed atmosphere of N2 and O2. Here, a flow rate of N2,
N2O or O2 is preferably in the range from about 100 to 6000
mL/min (sccm). Further, a flow rate ratio of N2 and O2, i.e.,
O2/N2, is preferably about 0 to 0.01. A processing pressure is
preferably higher than or equal to about 66.7 Pa, and more preferably in
the range from about 133.3 to 1333 Pa. A processing temperature is
preferably in the range from about 800 to 1200° C., and more
preferably in the range from about 800 to 1000° C. Processing time
is preferably in the range from about 0.5 to 2 minutes. After the
completion of the annealing of the step S4, the nitrogen and oxygen
profiles in the insulating film 306 are hardly changed, as illustrated in
FIG. 3D, compared to those measured after the completion of the step S3
(see FIG. 3C). However, since in Si--N bonds in the insulating film 306
can be cured by annealing, N losses which occur as time elapses are
reduced and a dense silicon oxynitride film of good quality can be
formed.

[0062]By performing the processes of the steps S1 to S4, it is possible to
form the insulating film 306 with a total film thickness smaller than or
equal to about 1 nm, and preferably about 0.5 to 1 nm. In this insulating
film 306, the fixed charges in the film and the interface states are
reduced and, also, the flat band potential Vfb is low. Therefore, when it
is used as a gate insulating film of a transistor, good ion
characteristics and a high Gm are obtained, and a Vth shift hardly
occurs, thereby achieving good electrical characteristics. By employing
the insulating film thus produced, a highly reliable device can be
fabricated.

[0063]Next, FIG. 4 shows a schematic configuration of a substrate
processing system 200 that can be preferably used to implement the gate
insulating manufacturing method of the present invention. A transfer
chamber 131 for transferring the wafer W is installed substantially at
the center of the substrate processing system 200. Disposed around the
transfer chamber 131 are the plasma processing apparatus 100 for
performing a plasma nitriding process on the wafer W, the heat treatment
apparatus 101 for performing on the wafer W a heat treatment including
thermal oxidation, a gate valve (not shown) for communication or block
between the processing chambers, and two load lock units 134 and 135 for
transferring the wafer W between the transfer chamber 131 and an
atmospheric transfer chamber 140.

[0064]Provided near the load lock units 134 and 135 are a preliminary
cooler unit 145 for performing a preliminary cooling operation and a
cooler unit 146 for performing a cooling operation. Further, when the
load lock units 134 and 135 are used as cooler units, it is not required
to install the preliminary cooler unit 145 and the cooler unit 146.

[0065]Transfer arms 137 and 138 are provided in the transfer chamber 131,
and transfer the wafer W with respect to each of the units.

[0066]Disposed in the atmospheric transfer chamber 140 connected to the
load lock units 134 and 135 are transfer units 141 and 142. The
atmospheric transfer chamber 140 is maintained in a clean environment by
a down-flowing clean air. The atmospheric transfer chamber 140 is
connected to a cassette unit 143, and the wafer W can be loaded and
unloaded with respect to four cassettes 144 set on the cassette unit 143
by the transfer units 141 and 142. Moreover, an alignment bar 147 is
provided adjacent to the atmospheric transfer chamber 140, and an
alignment of the wafer W is performed therein.

[0067]Each component of the substrate processing system 200 is controlled
by a process controller 150 having a CPU. The process controller 150 is
connected to a user interface 151 which includes a keyboard for a process
manager to input a command to operate the substrate processing system
200, a display for showing an operational status of the substrate
processing system 200, and the like.

[0068]Further, the process controller 150 is connected with a storage unit
152 for storing therein control programs (software) for implementing
various processes in the substrate processing system 200 under the
control of the process controller 150, and recipes including processing
condition data and the like.

[0069]If necessary, the process controller 150 executes a recipe read from
the storage unit 152 in response to instructions from the user interface
151, thereby implementing a required process in the substrate processing
system 200 under the control of the process controller 150. Moreover, the
control programs or the recipes such as the processing condition data and
the like can be stored in a computer-readable storage medium, e.g., a
CD-ROM, a hard disk, a flexible disk, a flash memory or the like, or
transmitted on-line from another device via, e.g., a dedicated line when
necessary.

[0070]FIG. 5 is a schematic cross sectional view showing an example of a
plasma processing apparatus 100 as a plasma nitriding unit in the
substrate processing system 200. This plasma processing apparatus 100 is
configured as an RLSA (radial line slot antenna) microwave plasma
processing apparatus capable of generating a microwave plasma of a high
density and a low electron temperature by introducing microwaves into a
processing chamber by using a planar antenna having a plurality of slots,
particularly an RLSA. Therefore, this plasma processing apparatus 100 can
perform a process using a plasma having a density ranging from about
1×1010 to 5×1012/cm3 and a low electron
temperature ranging from about 0.5 to 2 eV, and thus can be preferably
used to form a gate insulating film or the like in a manufacturing
process of various semiconductor devices such as a MOS
(Metal-Oxide-Silicon) transistor and the like.

[0071]When the plate 60 (to be described later) is employed, a low-damage
process can be performed by using a plasma having radical components of a
low electron temperature ranging from about 1 to 2 eV in a first plasma
region S1 and from about 0.5 to 1 eV in a second plasma region
S2.

[0072]The plasma processing apparatus 100 includes a substantially
cylindrical airtight chamber 1 that is grounded. A circular opening 10 is
formed at a substantially central portion of a bottom surface 1a of the
chamber 1, and an exhaust chamber 11 projecting downward is provided on
the bottom surface 1a while communicating with the opening 10.

[0073]A mounting table 2 made of ceramic, e.g., AlN or the like, is
provided in the chamber 1 to horizontally support a wafer W as a
substrate to be processed. Further, the mounting table 2 is supported by
a cylindrical supporting member 3 extending upward from a central bottom
portion of the exhaust chamber 11, the supporting member 3 being made of
ceramic, e.g., AlN or the like. A guide ring 4 for guiding the wafer W is
provided on an outer periphery portion of the mounting table 2.
Furthermore, a resistance heater 5 is buried in the mounting table 2 to
heat the mounting table 2 by a power supplied from a heater power supply
6. The wafer W as a substrate to be processed is heated by heat thus
generated. At this time, a heating temperature of the wafer W can be
controlled to be set between a room temperature and about 800° C.
In addition, a cylindrical liner 7 made of quartz is provided on an inner
periphery of the chamber 1. Besides, an annular baffle plate 8 having a
plurality of gas exhaust holes 8a is provided at a periphery of the
mounting table 2 to thereby uniformly exhaust the inside of the chamber
1. The baffle plate 8 is supported by a plurality of support columns 9.

[0074]The mounting table 2 is provided with wafer supporting pins (not
shown) for supporting and vertically moving the wafer W. The wafer
supporting pins can be protruded from or retracted into the top surface
of the mounting table 2.

[0075]Provided above the mounting table 2 is the plate 60 for reducing ion
energy in the plasma. By using this plate 60, when a silicon nitride film
having a thin film thickness smaller than or equal to, e.g., about 1 nm,
is formed, the controllability of a film thickness becomes good. This
plate 60 is made of a dielectric material such as ceramic, e.g., quartz,
sapphire, SiN, SiC, Al2O3, AlN or the like, or polysilicon,
single crystalline silicon, amorphous silicon or the like. In order to
prevent metal contamination, it is preferable to use a high purity
silicon-based material such as quartz, SiN, polysilicon, single
crystalline silicon, amorphous silicon or the like. Moreover, the plate
60 is supported by engaging an outer peripheral portion thereof with
support portions 70 projecting inward from the liner 7 in the chamber 1
along the entire circumference. Besides, the plate 60 may be supported in
a different manner.

[0076]Preferably, the plate 60 is attached near the wafer W. The distance
between the plate 60 and the wafer W (height H2) is preferably
ranging from, e.g., about 3 to 50 mm, and more preferably ranging from
about 25 to 35 mm. In this case, the distance between the top surface of
the plate 60 and the bottom surface of a is preferably ranging from,
e.g., about 30 to 150 mm, and more preferably ranging from about 50 to
100 mm. By installing the plate 60 at that location, silicon can be
nitrided uniformly while reducing plasma damage.

[0077]The space above the plate 60 serves as the first plasma region
S1, and the space below the plate 60 serves as the second plasma
region S2. It is preferable that the volume of the second plasma
region S2 is set to be the same as or smaller than the first plasma
region S1. The ratio between the height of the first plasma region
S1 and the height of the second plasma region S2, i.e.,
H1/H2, is preferably ranging from, e.g., about 0.6 to 50, and
more preferably ranging from about 1.4 to 4.

[0078]The plate 60 has a plurality of through holes 60a. FIGS. 6 and 7
illustrate the plate 60 in detail. FIG. 6 shows a top view of the plate
60, and FIG. 7 is a cross sectional view of a principal part of the plate
60.

[0079]The through holes 60a of the plate 60 are substantially uniformly
arranged so that the installation area of the through holes 60a is
slightly larger than the mounting area of the wafer W which is indicated
by a dashed line in FIG. 6. To be specific, in FIG. 6, the through holes
60a are arranged in an area enlarged outwardly from the outer periphery
of the wafer W so that a length L corresponding to a diameter of a circle
connecting the outer periphery of the arrangement area of the through
holes 60a with respect to the wafer W having a diameter of about 300 mm
is larger than a pitch of the through holes 60a by, e.g., a value ranging
from about 5 to 30 mm. Further, the through holes 60a can be arranged in
the entire surface of the plate 60. By arranging the through holes 60a in
a region wider than the wafer diameter, the nitriding process can be
uniformly performed.

[0080]A diameter D1 of the through holes 60a can be randomly varied.
For example, it is preferably ranging from about 2 to 15 mm, and more
preferably ranging from about 2.5 to 10 mm. Further, for example, a
diameter of each of the through holes 60a is about 10 mm in FIG. 6. The
diameters of the holes may be varied in accordance with the locations of
the through holes 60a in the plate 60. Moreover, the through holes 60a
may be arranged in a random pattern, e.g., a concentric circular pattern,
a radial pattern, a spiral pattern or the like. In addition, a thickness
T1 of the plate 60 is preferably, e.g., in the range from about 2 to
20 mm, and more preferably in the range from about 2 to 5 mm. By
specifying the diameter of the through holes 60a, it is possible to
reduce Vdc and ion damage to the wafer W. As a consequence, the
uniform nitriding process can be realized.

[0081]This plate 60 serves as an ion energy reducing device for reducing
the total amount of ion energy in the plasma.

[0082]That is, the plate 60 made of a dielectric material allows radicals
in the plasma to pass therethrough and blocks most of ions. To do so, it
is preferable to collectively consider an opening area of the through
holes 60a of the plate 60, the diameter D1 of the through holes 60a,
the shapes or the arrangement pattern of the through holes 60a, the
thickness T1 of the plate 60 (i.e., a height of a wall 60b), the
installation location of the plate 60 (a distance from the wafer W), as
will be described later. For example, when the opening diameter of the
through holes 60a is set to be in the range from about 2.5 to 10 mm, the
ratio of the opening area of the through holes 60a to the area of the
wafer W in the region of the plate 60 which corresponds to the wafer W
(i.e., region overlapped with the wafer W) is preferably ranging from
about 10 to 50%. By controlling the opening area ratio, the nitriding
process can be performed at a low Vdc while suppressing the ion
energy.

[0083]Although the single plate 60 is provided in the plasma processing
apparatus 100 shown in FIG. 5, two or more plates can be superposedly
provided if necessary. The opening area of the through holes 60a or the
ratio thereof can be properly adjusted depending on the processing
conditions, the object of the plasma nitriding process and the like.

[0084]An annular gas introducing member 15 is provided on a sidewall of
the chamber 1, and a gas supply system 16 is connected to the gas
introducing member 15. Further, the gas introducing member 15 may be
disposed in a form of a shower shape. The gas supply system 16 includes,
e.g., an Ar gas supply source 17, and an N2 gas supply source 18,
and these gases are supplied to the gas introducing member 15 through
respective gas lines 20, and then are introduced through the gas
introducing member 15 into the chamber 1. Each of the gas lines 20 is
provided with a mass flow controller 21 and opening/closing valves 22
disposed at an upstream and a downstream of the mass flow controller 21.
Instead of the N2 gas, as for a nitrogen containing gas, it is
possible to use, e.g., NH3 gas, gaseous mixture of N2 and
H2, hydrazine or the like. However, dangling bond defects are easily
caused by H, so that it is preferable to use a nitrogen containing gas
which does not contain hydrogen, such as N2 or the like. Further,
instead of the Ar gas, a rare gas such as Kr, Xe, He or the like can be
used.

[0085]A gas exhaust line 23 is connected on a side surface of the exhaust
chamber 11, and a gas exhaust unit 24 including a high speed vacuum pump
is connected with the gas exhaust line 23. By operating the gas exhaust
unit 24, a gas in the chamber 1 is uniformly discharged into a space 11a
of the exhaust chamber 11 and then is exhausted through the gas exhaust
line 23. Accordingly, the inside of the chamber 1 can be depressurized to
a predetermined vacuum level, e.g., 0.133 Pa, at a high speed.

[0086]Provided on the sidewall of the chamber 1 is a loading/unloading
port 25 for transferring the wafer W between the chamber 1 and a transfer
chamber (not shown) adjacent to the plasma processing apparatus 100 and a
gate valve 26 for opening and closing the loading/unloading port 25.

[0087]An upper portion of the chamber 1 has an opening, and a ring-shaped
support portion 27 is projected along a peripheral portion of the
opening. A microwave transmitting plate 28 made of a dielectric material,
e.g., quartz or ceramic such as Al2O3, AlN, or the like, is
airtightly disposed on the support portion 27 via a sealing member 29.
Therefore, the inside of the chamber 1 is airtightly maintained.

[0088]A circular plate-shaped planar antenna member 31 is provided on the
microwave transmitting plate 28 while facing the mounting table 2. The
planar antenna member 31 is fixed to a top portion of the sidewall of the
chamber 1. The planar antenna member 31 is made of, e.g., an aluminum
plate or a copper plate coated with gold or silver, and has a plurality
of slot-shaped microwave radiation holes 32 formed therethrough in a
predetermined pattern. For example, as shown in FIG. 8, the microwave
radiation holes 32 having pairs of holes of an elongated shape, and
typically, the microwave radiation holes 32 forming each of pairs are
disposed in a T shape. These pairs of microwave radiation holes 32 are
concentrically arranged.

[0089]A length of the microwave radiation hole 32 or an arrangement
interval therebetween is determined depending on a wavelength λg of
the microwave. For example, the microwave radiation holes 32 are spaced
apart from each other at the interval of λg/4, λg/2 or
λg. Further, in FIG. 8, the interval between the adjacent microwave
radiation holes 32 that are concentrically disposed is indicated as
Δr. Further, the microwave radiation holes 32 may have another
shape, e.g., a circular shape, an arc shape or the like. Further, the
microwave radiation holes 32 can be arranged in another pattern, e.g., a
spiral pattern, a radial pattern or the like, without being limited to
the concentric circular pattern.

[0090]Provided on the top surface of the antenna member 31 is a
retardation member 33 having a dielectric constant greater than that of a
vacuum. Since the wavelength of the microwave becomes longer in the
vacuum, the retardation member 33 has a function of controlling a plasma
by shortening the wavelength of the microwave. The planar antenna member
31 may be in contact with or separated from the microwave transmitting
plate 28 and the retardation member 33.

[0091]A shield lid 34 made of a metal material, e.g., aluminum, stainless
steel or the like, is provided on a top surface of the chamber 1 to cover
the planar antenna member 31 and the retardation member 33. The top
surface of the chamber 1 and the shield lid 34 are sealed by sealing
members 35. Cooling water paths 34a are formed in the shield lid 34. By
circulating cooling water therethrough, it is possible to cool the shield
lid 34, the retardation member 33, the planar antenna member 31 and the
microwave transmitting plate 28. Further, the shield lid 34 is grounded.

[0092]The shield lid 34 has an opening 36 at a center of a top wall
thereof, and a waveguide 37 is connected with the opening. A microwave
generating device 39 for generating microwaves is connected with an end
portion of the waveguide 37 via a matching circuit 38. Accordingly, a
microwave having a frequency of, e.g., 2.45 GHz, which is generated from
the microwave generating device 39, is propagated to the antenna member
31 via the waveguide 37. The microwave may have a frequency of 8.35 GHz,
1.98 GHz or the like.

[0093]The waveguide 37 includes a coaxial waveguide 37a having a circular
cross section and extending upward from the opening 36 of the shield lid
34, and a rectangular waveguide 37b extending in a horizontal direction
and connected with an upper portion of the coaxial waveguide 37a via a
mode transducer 40. The mode transducer 40 between the rectangular
waveguide 37b and the coaxial waveguide 37a has a function of converting
a TE mode of the microwave propagating in the rectangular waveguide 37b
into a TEM mode. An internal conductor 41 is extended in the coaxial
waveguide 37a, and a lower portion of the internal conductor 41 is
fixedly connected to a center of the antenna member 31. As a consequence,
the microwave is efficiently and uniformly propagated to the antenna
member 31 via the internal conductor 41 of the coaxial waveguide 37a
radially.

[0094]In the RLSA plasma processing apparatus 100 configured as described
above, the process for forming a silicon nitride film by directly
nitriding the silicon layer of the wafer W and the like can be performed
in following sequences.

[0095]First of all, the wafer W on which a silicon layer is formed is
loaded through the loading/unloading port 25 into the chamber 1 by
opening the gate valve 26 and then mounted on the mounting table 2. Next,
Ar gas and N2 gas are respectively introduced at predetermined
respective flow rates from the Ar gas supply source 17 and N2 gas
supply source 18 into the chamber 1 through the gas introducing member
15. Further, a pressure in the chamber 1 is adjusted to a predetermined
level, and a temperature of the wafer W is heated to a predetermined
level.

[0096]Next, the microwave from the microwave generating device 39 is
transmitted to the waveguide 37 via the matching unit 38. The microwave
is supplied to the planar antenna member 31 via the rectangular waveguide
37b, the mode transducer 40, the coaxial waveguide 37a and the internal
conductor 41 in that order, and then is emitted from the holes 32 (slots)
of the planar antenna member 31 toward a space above the wafer W in the
chamber 1 through the microwave transmitting plate 28. The microwave
propagates in the rectangular waveguide 37b in the TE mode. The TE mode
of the microwave is converted into the TEM mode in the mode transducer
40, and the microwave propagates in the TEM mode through the coaxial
waveguide 37a toward the antenna member 31. At this time, it is
preferable that the power of the microwave generating device 39 is, e.g.,
in a range from about 0.5 to 5 kW.

[0097]An electromagnetic field is formed in the chamber 1 by the
microwaves emitted from the planar antenna member 31 into the chamber 1
via the microwave transmitting plate 28, thereby converting Ar gas and
N2 gas into a plasma. By emitting the microwaves through the
plurality of holes 32 of the planar antenna member 31, the microwave
plasma has a high density ranging from about 1×1010/cm3
to 5×1012/cm3 and an electron temperature lower than or
equal to about 1.5 eV near the wafer W.

[0098]The microwave plasma thus generated causes less plasma damage due to
ions and the like to the base film. Further, by providing the dielectric
plate 60 having through holes in the chamber 1, the first plasma region
S1 for generating a plasma and the second plasma region S2 for
processing the wafer W by the plasma that has passed through the plate 60
are separately provided. Accordingly, the ion energy in the second plasma
region S2 is greatly reduced, and the sheath voltage Vdc near
the substrate can be decreased. In addition, the electron temperature of
the plasma can be reduced to be about 1 eV or less and more preferably to
be about 0.7 eV or less. As a result, the plasma damage can be further
reduced.

[0099]Further, N can be directly introduced into the silicon by an action
of active species, mainly nitrogen radicals N* and the like, in the
plasma, so that a uniform SiN film can be formed.

[0100]Next, FIG. 9 is a schematic diagram of the heat treatment apparatus
101 as a heat treatment unit in the substrate processing system 200. The
heat treatment apparatus 101 is configured as a single wafer RTP (Rapid
Thermal Processing) apparatus for performing an RTA (Rapid Thermal
Annealing) with high controllability, and can be used to perform, e.g.,
annealing or thermal oxidation, on a thin film formed on the wafer W at a
high temperature in the range from about 800 to 1200° C.

[0101]Besides, the heat treatment apparatus is not limited to a single
substrate heat treatment apparatus, and may be a batch-type heat
treatment apparatus capable of processing a plurality of substrates
simultaneously.

[0102]In FIG. 9, a reference number 71 indicates a cylindrical processing
chamber, and a lower heating unit 72 is detachably provided on the bottom
of the processing chamber 71. Further, an upper heating unit 74 is
detachably provided on the top of the processing chamber 71 to face the
lower heating unit 72. The lower heating unit 72 includes a plurality of
tungsten lamps 76 as heating units disposed on a top surface of a cooling
jacket 73 where a cooling water path (not shown) is formed. In the same
manner, the upper heating unit 74 has a water cooling jacket 75 where a
cooling water path (not shown) is formed and a plurality of tungsten
lamps 76 disposed on a bottom surface thereof. In addition, as for the
lamp, it is possible to use, e.g., a halogen lamp, a Xe lamp, a mercury
lamp, a flash lamp or the like, other than the tungsten lamp 76. The
tungsten lamps 76 arranged to face each other in the processing chamber 1
are connected to a power supply (not shown) and a control unit (process
controller 150) for controlling power supplied therefrom, so that the
heat discharge rate can be controlled.

[0103]A supporting portion 77 for supporting the wafer W is provided
between the lower heating unit 72 and the upper heating unit 74. The
supporting portion 77 includes a wafer supporting pin 77a for supporting
the wafer W maintained in a processing space of the processing chamber 71
and a liner mounting portion 77b for supporting a hot liner 78 for
measuring a temperature of the wafer W during the processing. Further,
the supporting portion 77 is connected to a rotation mechanism (not
shown) which rotates the entire supporting portion 77 about a vertical
axis. Accordingly, the wafer W rotates at a predetermined speed during
the processing, and the uniformity of the heat treatment is realized.

[0104]A pyrometer 81 is disposed below the chamber 71. By measuring heat
rays from the hot liner 78 via a port 81a and an optical fiber 81b with
the use of the pyrometer 81 during the heat treatment, the temperature of
the wafer W can be measured indirectly. Further, the temperature of the
wafer W can be measured directly.

[0105]In addition, a quartz member 79 is arranged between the bottom of
the hot liner 78 and the tungsten lamps 76 of the lower heating unit 72,
and is provided with the port 81a, as illustrated. Further, a plurality
of ports 81a may be provided.

[0106]Further, a quartz member 80a is arranged between the wafer W and the
tungsten lamps 76 of the upper heating unit 74. Also, a quartz member 80b
is disposed on an inner peripheral surface of the chamber 71 to surround
the wafer W.

[0107]Moreover, a lifter pin (not shown) for supporting and vertically
moving the wafer W is provided to penetrate the hot liner 78, and is used
to load and unload the wafer W.

[0108]Sealing members (not shown) are provided between the lower heating
unit 72 and the processing chamber 71 and between the upper heating unit
74 and the processing chamber 71, and the inside of the processing
chamber 71 is maintained at an airtight state.

[0109]Further, a gas supply source 83 connected to a gas inlet line 82 is
disposed at a side portion of the processing chamber 71, so that gases
such as N2O gas, O2 gas, Ar gas and the like can be introduced
into the processing space of the processing chamber 71. Furthermore, a
gas exhaust line 84 is provided at a lower portion of the processing
chamber 71, so that the inside of the processing chamber 71 can be
depressurized by a gas exhaust unit (not shown).

[0110]In the heat treatment apparatus 101 configured as described above,
after the wafer W is set on the wafer supporting portion 77 in the
processing chamber 71, an airtight space is formed. Next, the tungsten
lamps 76 of the lower heating unit 72 and the upper heating unit 74 are
turned ON by supplying a predetermined power (not shown) from the power
supply (not shown) thereto under the control of the process controller
150, so that heat is generated from each of the tungsten lamps 76. The
heat rays thus generated are irradiated to the wafer W via the quartz
members 79 and 80a. The wafer W is rapidly heated from the above and
below thereof based on the recipe (heating rate, heating temperature and
the like) while being rotated. While the wafer W is heated, the gas
exhaust unit (not shown) is driven to discharge gases through the gas
exhaust line 84, thereby depressurizing the inside of the chamber 71.

[0111]The wafer W is rotated by rotating the entire supporting portion 77
about a vertical axis at a predetermined rotation speed by a rotation
mechanism (not shown) during the heat treatment. As a result, the
uniformity of the heat supplied to the wafer W is ensured.

[0112]Further, during the heat treatment, the temperature of the hot liner
78 can be measured by the pyrometer 81, and the temperature of the wafer
W can be measured indirectly. The temperature data measured by the
pyrometer 81 is feedback to the process controller 150. When the measured
temperature is different from the set temperature in the recipe, the
power supplied to the tungsten lamps 76 is adjusted through the control
of the process controller 150.

[0113]After the heat treatment is completed, the lower heating unit 72,
the upper heating unit 74 and the tungsten lamps 76 are turned OFF.
Further, a purge gas such as an inert gas, e.g., nitrogen or the like, is
introduced through a purge port (not shown) into the processing chamber
71, while discharging gases through the gas exhaust line 84, thereby the
wafer W is cooled. Thereafter, the cooled wafer W is unloaded from the
processing chamber 71.

[0114]In the substrate processing system 200 configured as described
above, a series of processes of the steps S1 and S2, preferably steps S1
to S3, and more preferably steps S1 to S4 shown in FIG. 1 are executed,
thereby forming the high-quality insulating film 306 on a surface of
silicon such as single crystalline silicon or polycrystalline silicon.

[0115]That is, first of all, the wafer W is received from any one of the
cassettes 144 on the cassette unit 143 by the transfer unit 141 or 142 of
the atmospheric transfer chamber 140, and then is loaded into any one of
the load lock units 134 and 135. After the inside of the load lock unit
134 or 135 is depressurized, the wafer W is unloaded from the load lock
unit 134 or 135 by using the transfer arm 137 or 138 into the transfer
chamber 131, and then is loaded into the plasma processing apparatus 100.
Next, the first nitriding process of the step S1 is performed under the
processing conditions described above. After the first nitriding process
is completed, the wafer W is unloaded from the plasma processing
apparatus 100 by the transfer arm 137 or 138, and then is loaded into the
heat treatment apparatus 101. Then, the oxidation process of the step S2
is performed by the heat treatment apparatus 101 under the
above-described processing conditions.

[0116]Upon completion of the oxidation process, the processes of the steps
S3 and S4 may be executed consecutively. In this case, the wafer is
unloaded from the heat treatment apparatus 101 by the transfer arm 137 or
138, and then is loaded into the plasma processing apparatus 100.
Further, the second nitriding process of the step S3 is performed in the
plasma processing apparatus 100 under the processing conditions described
above. After the second nitriding process is completed, the wafer W is
unloaded from the plasma processing apparatus 100 by the transfer arm 137
or 138, and then is loaded into the heat treatment apparatus 101. Then,
the annealing of the step S4 is performed under the above-described
processing conditions.

[0117]When all the processes are completed, the wafer W is unloaded from
the heat treatment apparatus 101 by the transfer arm 137 or 138, and then
is loaded into any one of the load lock units 134 and 135. Further, the
inside of the load lock unit 134 or 135 is set to the atmospheric
pressure. Next, the wafer W is unloaded from the load lock unit 134 or
135 by the transfer unit 141 or 142 of the atmospheric transfer chamber
140, and then is returned to any one of the cassettes 144 in the cassette
unit 143. In this manner, a series of processes for a single wafer W are
completed. This system enables the processing to be performed in a vacuum
state without being exposed to the atmosphere. Accordingly, the
insulating film can be formed without causing contamination from organic
materials and the like.

[0118]The insulating film 306 thus formed can be used as a gate insulating
film formed of a silicon oxynitride film in manufacturing various
semiconductor devices such as a transistor and the like. As a preferred
prospect thereof, it is particularly useful to form a thin film in a next
generation device, e.g., a gate insulating film having a film thickness
of less than about 1 nm and preferably in a range from about 0.5 to 1 nm.
FIGS. 10A to 10C provide process cross sectional views for explaining an
example to which the plasma nitriding processing method of the present
invention is applied.

[0119]As illustrated in FIG. 10A, a well (not shown) is formed on a P-type
or an N-type silicon substrate 401, and a device isolation layer 402 is
formed by, e.g., a LOCOS method. Further, the device isolation layer 402
may be formed by an STI (Shallow Trench Isolation) method.

[0120]Next, as shown in FIG. 10B, a gate insulating film 403 is formed on
a surface of the silicon substrate 401 in accordance with the sequences
of the steps S1 to S4 shown in FIG. 1. Although a film thickness of the
gate insulating film 403 varies depending on target devices, it is
preferably ranging from about 0.5 to 1 nm.

[0121]Further, a polysilicon layer 404 is formed on the gate insulating
film 403 by a CVD at a temperature higher than, e.g., about 400°
C. Next, etching is performed by using a mask having a pattern formed by
a photolithography technique, to form a gate electrode. Further, a gate
electrode structure is not limited to a single layer structure of the
polysilicon layer 404, but may be a polycide structure including a
silicide of, e.g., tungsten, molybdenum, tantalum, titanium, cobalt,
nickel or the like, to reduce a specific resistance of the gate electrode
and obtain high operation speed. After the gate electrode is formed, a
source/drain (not shown) is formed by performing ion implantation and
activation, and a sidewall 405 of an insulating film such as SiO2,
SiN or the like is formed, thereby fabricating a transistor 400 having a
MOS structure shown in FIG. 10C.

[0122]Hereinafter, test results for confirming the effects of the present
invention will be described.

[0123]A silicon nitride film (SiN film) was formed on a surface of single
crystalline silicon of a wafer W by using the plasma processing apparatus
100 having a configuration shown in FIG. 5. The plasma nitriding process
was performed under the following conditions: a processing gas of Ar gas
and N2 gas respectively having flow rates of 1000/200 mL/min(sccm);
a wafer temperature set at about 600° C.; a processing pressure of
about 199.9 Pa (1500 mTorr); a microwave power of about 1.5 kW; and
processing time of about 36 seconds. As for the plate 60 of the plasma
processing apparatus, there was used one having through holes 60a having
diameters of about 9.5 mm, 9.7 mm and 11 mm.

[0124]Next, the wafer W having the silicon nitride film (SiN film) was
thermally treated (first annealing process) in an N2O atmosphere by
using the heat treatment apparatus 101 having a configuration shown in
FIG. 9. As a consequence, a silicon nitride film (SiON film) was formed.
The following conditions were applied to the thermal oxidation process: a
processing gas of an N2O gas having a flow rate of about 2
L/min(slm); a wafer temperature set at about 1100° C.; and a
processing pressure of about 133.3 Pa (1 Torr). For comparison, a wafer W
having a silicon nitride film (SiN film) was thermally treated in an
O2 atmosphere, instead of in an N2O atmosphere, to form a
silicon nitride film (SiON film). At this time, the following conditions
were applied: a processing gas of an O2 gas having a flow rate of
about 2 L/min(slm); a wafer temperature set at about 1100° C.; and
a processing pressure of about 666.65 Pa (5 Torr).

[0125]The distribution of oxygen atoms (O1s) and nitrogen atoms (N1s) in
the silicon oxynitride film (SiON film) in a film thickness direction was
measured by using an angle resolved X-ray photoelectron spectroscopy
(AR-XPS). Results thereof are shown in FIGS. 11A and 11B. In FIG. 11A,
the vertical axis indicates concentration of normalized oxygen atoms
(O1s), and the horizontal axis indicates a normalized depth. A scale of 0
indicates a surface, and a scale of 1 indicates an SiON--Si interface in
which Si concentration is 50%. Further, in FIG. 11B, the vertical axis
represents concentration of normalized nitrogen atoms (N1s), and the
horizontal axis represents a normalized depth. A scale of 0 indicates a
surface, and a scale of 1 indicates an SiON--Si interface in which Si
concentration is 50%. Also, FIGS. 11A and 11B indicate concentration of
normalized silicon atoms (Si2p).

[0126]From the results shown in FIGS. 11A and 11B, it is found that, when
the heat treatment was performed in the N2O atmosphere, compared to
when it was performed in the O2 gas atmosphere, a small amount of
oxygen atoms (O1s) was distributed near the surface of the silicon
oxynitride film (SiON film), and a large amount of oxygen atoms (O1s) was
distributed near the interface with the silicon. The reason that the film
quality varies depending on the processing gases is because the diffusion
movement of oxygen atoms in the silicon nitride film (SiN film) is
different between the oxidation process using an N2O gas and the
oxidation process using an O2 gas.

[0127]Further, as shown in FIG. 11A, the silicon oxynitride film thermally
oxidized by using an N2O gas has an oxygen concentration gradient
gradually decreasing from a surface side toward an SiON--Si interface in
a film thickness direction, and shows a profile in which oxygen of
certain amount exists at the SiON--Si interface. Furthermore, FIG. 11B
shows a nitrogen concentration gradient in a film depth direction, and
thus, FIGS. 11A and 11B present profiles in which oxygen and nitrogen
(SiON) exist in the interface regions. Further, the silicon oxynitride
film thermally oxidized by using an N2O gas shows a profile in which
the large amount of oxygen atoms (O1s) are distributed in the SiON--Si
interface, compared to the silicon oxynitride film thermally oxidized by
using an O2 gas. By introducing oxygen into the SiON--Si interface,
fixed charges are reduced, and the interface state decreases.
Accordingly, the mobility of carriers in the transistor having this
silicon oxynitride film as a gate insulating film is improved. Further,
Gm or ion characteristics are improved, and a Vth shift is suppressed.
Besides, leakage current density Jg decreases, so that a leakage current
can be suppressed.

[0128]Next, a MOS transistor was fabricated by using the silicon nitride
film as a gate insulating film, and the electrical characteristics
thereof were examined.

[0129]In this test, a silicon nitride film (SiN film) was formed on a
surface of single crystalline silicon of a wafer W by using the plasma
processing apparatus 100 having a configuration shown in FIG. 5. The
following conditions were applied to the plasma processing: a processing
gas of mixture of Ar and N2 respectively having flow rates of
Ar/N2=1000/200 mL/min(sccm); a wafer temperature set at about 600°
C.; a processing pressure of about 199.9 Pa (1500 mTorr); a microwave
power of about 1.5 kW; and processing time of about 36 seconds.

[0130]Next, the wafer W having the silicon nitride film (SiN film) was
thermally oxidized by using the heat treatment apparatus 101 having a
configuration shown in FIG. 9, thereby forming a silicon oxynitride film
(SiON film). The thermal oxidation was carried out under the following
conditions to vary nitrogen concentration in the silicon oxynitride film
(SiON film).

[0131]<Condition 1: in-Film Nitrogen Concentration of 30%>

[0132]a processing pressure of about 266.6 Pa (2 Torr); a processing gas
having a mixture of N2 and N2O respectively having flow rates
of about 1.7/0.3 L/min(slm); a processing temperature set at about
1100° C.; and processing time of about 10 seconds

[0133]<Condition 2: in-Film Nitrogen Concentration of 23%>

[0134](i) a processing pressure of about 266.6 Pa (2 Torr); a processing
gas having a mixture of N2 and N2O respectively having flow
rates of about 1.7/0.3 L/min(slm); a processing temperature set at about
1100° C.; and processing time of about 23 seconds

[0135](ii) a processing pressure of about 666.5 Pa (5 Torr); a processing
gas of O2 having a flow rate of about 2 L/min(slm); a processing
temperature set at about 1100° C.; and processing time of about 15
seconds

[0136](iii) a processing pressure of about 666.5 Pa (5 Torr); a processing
gas having a mixture of N2 and N2O respectively having flow
rates of about 1.7/0.3 L/min(slm); a processing temperature set at about
900° C.; and processing time of about 25 seconds

[0137]<Condition 3: in-Film Nitrogen Concentration of 20%>

[0138](i) a processing pressure of about 133.3 Pa (1 Torr); a processing
gas of N2O having a flow rate of about 2 L/min(slm); a processing
temperature set at about 1100° C.; and processing time of about 23
seconds

[0139](ii) a processing pressure of about 9997.5 Pa (75 Torr); a
processing gas of O2 having a flow rate of about 2 L/min(slm); a
processing temperature set at about 1100° C.; and processing time
of about 9 seconds

[0140]<Condition 4: in-Film Nitrogen Concentration of 15%>

[0141]a processing pressure of about 666.5 Pa (5 Torr); a processing gas
of N2O having a flow rate of about 2 L/min(slm); a processing
temperature set at about 1100° C.; and processing time of about 23
seconds

[0142]<Condition 5: in-Film Nitrogen Concentration of 10%>

[0143]a processing pressure of about 9997.5 Pa (75 Torr); a processing gas
of N2O having a flow rate of about 2 L/min(slm); a processing
temperature set at about 1100° C.; and processing time of about 14
seconds

[0144]<Condition 6: in-Film Nitrogen Concentration of 18%>

[0145]a processing pressure of about 9997.5 Pa (75 Torr); a processing gas
of N2O having a flow rate of about 2 L/min(slm); a processing
temperature controlled at about 900° C.; and processing time of
about 19 seconds

[0146]FIG. 12 shows a relationship between an SiO2 equivalent
thickness (EOT) of a gate insulating film and a maximum value of a
transfer conductance (Gmmax). From FIG. 12, it can be found that
Gmmax greatly varied depending on oxidation conditions. When a
silicon oxynitride film (SiON film) formed at a processing temperature of
about 1100° C. by using an N2O gas as a processing gas for
oxidation was used as a gate insulating film, compared to when a silicon
oxynitride film formed by using an O2 gas was used, a significantly
high Gmmax was obtained at the same EOT, which verified that good
electrical characteristics were obtained. That is, by using an N2O
gas, the Gmmax can be increased without increasing an EOT and the
ion characteristics can be improved.

[0147]When an N2O gas was used as a processing gas, a higher
Gmmax and better electrical characteristics were obtained in the
case of using as a gate insulating film a silicon oxynitride film (SiON
film) thermally oxidized at about 1100° C. than in the case of
using as a gate insulating film a silicon oxynitride film thermally
oxidized at about 900° C.

[0148]From the above results, it can be found that an N2O gas is
preferably used for a thermal oxidation process for oxidizing a silicon
nitride film, and the thermal oxidation process is preferably performed
at a temperature higher than about 900° C., preferably in the
range from about 1000 to 1200° C., for a short period of time in
the range from about 5 to 60 seconds. Further, it can be found that the
N2O partial pressure is preferably in the range from about 3.3 to
133.3 Pa.

[0149]Then, the effects of the processing temperature to the electrical
characteristics of the transistor in the thermal oxidation process (step
S2) using an N2O gas were examined by the following method.

[0150]First of all, a surface of single crystalline silicon of a wafer W
was processed by a 1% dilute hydrofluoric acid (DHF) and, then, a plasma
nitriding process was performed by using the plasma processing apparatus
100 having a configuration shown in FIG. 5. Accordingly, a silicon
nitride film (SiN film) was formed on the silicon surface. The plasma
nitriding process was performed under the following conditions: a
processing gas having a mixture of Ar and N2 respectively having
flow rates of about 1000/200 mL/min(sccm); a wafer temperature set at
about 400° C.; a processing pressure in the range from about 6.7
to 199.9 Pa (in the range about 50 to 1500 mTorr); a microwave power of
about 1.5 kW; and processing time of about 50 seconds.

[0151]Next, the wafer W having the silicon nitride film (SiN film) was
thermally oxidized by using the heat treatment apparatus 101 having a
configuration shown in FIG. 9, thereby forming a silicon oxynitride film
(SiON film). The thermal oxidation was carried out under the following
conditions: a processing pressure in the range from about 40 to 1333 Pa
(in the range from about 300 mTorr to 10 Torr); a processing gas of
N2O having a flow rate of 2 L/min(sccm); varied processing
temperatures of about 1000° C., 1050° C. or 1100°
C.; and processing time ranging from about 10 to 70 seconds. Then, an
NMOS transistor having as a gate insulating film the silicon nitride film
(SiON film) thus formed was fabricated, and Gmmax and Jg at a gate
voltage of +1.1 V were measured.

[0152]FIG. 13 represents a relationship between Gmmax and a
processing temperature, and FIG. 14 represents a relationship between Jg
and a processing temperature. Further, the vertical axis shown in FIG. 13
indicates a percentage when setting as 100% Gmmax of the NMOS
transistor using a silicon oxide film (SiO2 film) as a gate
insulating film. Moreover, FIG. 14 indicates a normalized Jg of the NMOS
transistor using a silicon oxide film (SiO2 film) as a gate
insulating film. The horizontal axes shown in FIGS. 13 and 14 represent
the temperature of the thermal oxidation process.

[0153]From FIG. 13, it can be (found that Gmmax increased as the
processing temperature of the thermal oxidation using N2O increased.
This is considered because, as the processing temperature increased, the
amount of oxygen reaching the interface between the silicon oxynitride
film and the silicon layer increased and the fixed charges at the
interface were reduced. Moreover, from FIG. 14, it can be found that Jg
was substantially constant regardless of the processing temperature of
the thermal oxidation process. Therefore, it is clear that the thermal
oxidation process (annealing) of the step S2 is preferably performed at a
high temperature higher than or equal to about 1000° C., e.g., in
a range from about 1000 to 1200° C., and more preferably at a
temperature higher than or equal to about 1050° C.

[0154]Next, the effects of the processing pressure of the nitriding
process in the step S3 for nitriding the surface side of the silicon
oxynitride film (SiON film) to the profile of atoms in the film were
examined by the following method.

[0155]Above all, a surface of single crystalline silicon of a wafer W was
processed by a 1% dilute hydrofluoric acid (DHF) and, then, a plasma
nitriding process was performed by using the plasma processing apparatus
100 having a configuration shown in FIG. 5. Accordingly, a silicon
nitride film (SiN film) was formed on the silicon surface. The plasma
nitriding process was performed under the following conditions: a
processing gas having a mixture of Ar and N2 respectively having
flow rates of about 1000/40 mL/min(sccm); a wafer temperature set at
about 400° C.; a processing pressure of about 199.9 Pa (about 1500
mTorr); and a microwave power of about 1.5 kW.

[0156]Next, the wafer W having the silicon nitride film (SiN film) was
thermally oxidized by using the heat treatment apparatus 101 having a
configuration shown in FIG. 9, thereby forming a silicon oxynitride film
(SiON film). The thermal oxidation was carried out under the following
conditions: a processing pressure of about 213 Pa (1600 mTorr); a
processing gas having a mixture of N2 and N2O respectively
having flow rates of about 1700/300 mL/min(sccm); a processing
temperature of about 1100° C.; and processing time of about 30
seconds.

[0157]Thereafter, the surface side of the silicon oxynitride film was
mainly subjected to plasma nitriding by using the plasma processing
apparatus 100 having a configuration shown in FIG. 5. The plasma
nitriding process was performed under the following conditions: a
processing gas having a mixture of Ar and N2 respectively having
flow rates of about 1000/40 mL/min(sccm); a wafer temperature set at
about 400° C.; varied processing pressures of about 6.7 Pa (50
mTorr), 19.9 Pa (150 mTorr), 45.0 Pa (338 mTorr) or 66.7 Pa (500 mTorr);
and a microwave power ranging from 1.0 to 1.5 kW.

[0158]FIG. 15 shows a relationship between a film thickness and an N
concentration in a film in an XPS analysis. A notation of "non-step3" in
FIG. 15 indicates a case where the steps S1 and S2 of FIG. 1 were
performed without performing the step S3. Besides, FIGS. 16A to 16C
illustrate profiles of nitrogen atoms (N1s), oxygen atoms (O1s) and
silicon atoms (Si2P) in the film. In FIGS. 16A to 16C, a curve A
indicates a case where the processes up to the step S2 were performed
without performing the processes thereafter; a curve B indicates a case
where the second nitriding process of the step S3 was performed at about
6.7 Pa (50 mTorr); and a curve C represents a case where the second
nitriding process of the step S3 was performed at about 66.7 Pa (500
mTorr).

[0159]From FIG. 15, it is clear that, when the nitriding process of the
step S3 was performed at a low pressure (e.g., about 6.7 Pa), compared to
when it was performed at a relatively high pressure (e.g., about 66.7
Pa), the nitrogen concentration was higher at the same film thickness
and, hence, a film growth was suppressed. Further, from FIGS. 16A to 16C,
it is clear that, when the nitriding process of the step S3 was performed
at a low pressure (e.g., about 6.7 Pa), it was possible to increase the
nitrogen concentration near the surface of the silicon oxynitride film.
Accordingly, it is expected to reliably prevent a leakage current of a
transistor having a silicon oxynitride film as a gate insulating film.
That is, it is preferable to perform the nitriding process of the step S3
at a pressure between about 0.133 and 66.7 Pa.

[0160]Thereafter, there were examined the effects of
performance/non-performance of the annealing process of the step S4 and
conditions of the corresponding annealing process to the electrical
characteristics of the transistor. By processing the wafer W under the
following condition, an insulating film (silicon oxynitride film) was
formed. Next, a transistor having the insulating film as a gate
insulating film was fabricated, and the electrical characteristics
thereof were examined.

[0161]<Pre-Treatment>

[0162]The treatment using 1% dilute hydrofluoric acid (DHF) was performed
for about 45 seconds.

[0163]<Nitriding Process 1 (Step S1)>

[0164]The plasma nitriding process (first plasma nitriding process) was
performed by using the plasma processing apparatus 100 having a
configuration shown in FIG. 5 under the following conditions: a
processing gas having a mixture of Ar and N2 respectively having
flow rates of about 1000/200 mL/min (sccm); a wafer temperature
controlled at about 600° C.; a processing pressure of about 199.9
Pa (1500 mTorr); and a microwave power of about 1.5 kW.

[0165]<Oxidation Process A1 (Step S2)>

[0166]The thermal oxidation process (first annealing process (N2O))
was performed by using the heat treatment apparatus 101 having a
configuration shown in FIG. 9 under the following conditions: a
processing gas of N2O having a flow rate of about 2000 mL/min
(sccm); a processing temperature controlled at about 1100° C.; and
processing time of about 23 seconds.

[0167]<Oxidation Process A2 (Step S2)>

[0168]The thermal oxidation process (first annealing process (O2))
was performed by using the heat treatment apparatus 101 having a
configuration shown in FIG. 9 under the following conditions: a
processing gas of O2 having a flow rate of about 2000 mL/min (sccm);
a processing pressure of about 9997.5 Pa (75 Torr); a processing
temperature controlled at about 1100° C.; and processing time of
about 9 seconds.

[0169]<Nitriding Process 2 (Step S3)>

[0170]The plasma nitriding process (second plasma nitriding process) was
performed mainly on the surface side of the silicon oxynitride film by
using the plasma processing apparatus 100 having a configuration shown in
FIG. 5 under the following conditions: a processing gas having a mixture
of Ar and N2 respectively having flow rates of about 1000/40 mL/min
(sccm); a wafer temperature controlled at about 600° C.; a
processing pressure of about 12 Pa (90 mTorr); a microwave power of about
1.5 kW; and processing time of about 23 seconds.

[0171]<Annealing Process A1 (Step S4)>

[0172]The annealing process (second annealing process) was performed by
using the heat treatment apparatus 101 having a configuration shown in
FIG. 9 under the following conditions: a processing gas of N2 having
a flow rate of about 2000 mL/min (sccm); a processing pressure of about
133.3 Pa (1 Torr); a processing temperature controlled at about
800° C.; and processing time of about 30 seconds.

[0173]<Annealing Process A2 (Step S4)>

[0174]The annealing process (second annealing process) was performed by
using the heat treatment apparatus 101 having a configuration shown in
FIG. 9 under the following conditions: a processing gas of N2 having
a flow rate of about 2000 mL/min (sccm); a processing pressure of about
133.3 Pa (1 Torr); a processing temperature controlled at about
1000° C.; and processing time of about 30 seconds.

[0175]<Annealing Process A3 (Step S4)>

[0176]The annealing process (second annealing process) was performed by
using the heat treatment apparatus 101 having a configuration shown in
FIG. 9 under the following conditions: a processing gas having a mixture
of O2 and N2 respectively having flow rates of about 100/1900
mL/min (sccm); a processing pressure of about 133.3 Pa (1 Torr); a
processing temperature controlled at about 1100° C.; and
processing time of about 30 seconds.

[0177]Test 1:

[0178]The processes were performed in the order of the pre-treatment, the
nitriding process 1 (first plasma nitriding process) and the oxidation
process A2 (first annealing process) (without performing the processes
after the step S2).

[0179]Test 2:

[0180]The processes were performed in the order of the pre-treatment, the
nitriding process 1 (first plasma nitriding process) and the oxidation
process A1 (first annealing process) (without performing the processes
after the step S2).

[0181]Test 3:

[0182]The processes were performed in the order of the pre-treatment, the
nitriding process 1 (first plasma nitriding process), the oxidation
process A1 (first annealing process) and the nitriding process 2 (second
plasma nitriding process) (without performing the step S4).

[0189]The measurement results of Gmmax and Jg in the tests 1 to 6 are
shown in FIGS. 17 and 18, respectively. Further, the vertical axis of
FIG. 17 indicates a percentage when setting as 100% Gmmax of the
NMOS transistor using a silicon oxide film (SiO2 film) as a gate
insulating film. Moreover, the vertical axis of FIG. 18 indicates a
normalized Jg of the NMOS transistor using a silicon oxide film
(SiO2 film) as a gate insulating film.

[0190]From FIG. 17, it is seen that when the tests 1 and 2 in which the
processes after the step S3 were not performed were compared, Gmmax
was greatly increased in the test 2 in which the thermal oxidation
process of the step S2 was performed by using N2O, compared to that
in the test 1 in which the thermal oxidation process of the step S2 was
performed by using O2. Further, Gmmax in the test 2 was
substantially the same as that in the test 3 in which the nitriding
process of the step S3 was carried out.

[0191]Moreover, the test 3 in which the processes up to the nitriding
process of the step S3 were performed was compared with the tests 4 to 6
in which the processes up to the annealing process of the step S4 were
performed. In the test 4 in which the annealing process was performed in
an N2 atmosphere and at about 800° C., there was obtained
Gmmax substantially the same as that in the test 3 in which the
annealing process was not executed, and an insulating film having good
electrical characteristics was formed. Further, in the tests 5 and 6 in
which the annealing process of the step S4 was performed at a temperature
higher than or equal to 1000° C., Gmmax was greatly improved
regardless of types of purge gases, and an insulating film having better
electrical characteristics was formed.

[0192]From FIG. 18, it is seen that Jg was decreased and, thus, a leakage
current was suppressed in the test 3 in which the processes were
performed up to the nitriding process of the step S3 and the tests 4 to 6
in which the processes were performed up to the annealing process of the
step S4, compared to those in the tests 1 and 2 in which the processes
after the step S2 were not performed. Therefore, it is possible to form
an insulating film having good electrical characteristics. Further, in
the annealing process of the step S4, the flow rate ratio of
O2/N2 is preferably in a range from about 0 to 0.01. It is more
preferable to perform the annealing process in an 100% N2 gas
atmosphere.

[0193]Further, the present invention is not limited to the above
embodiments, and may be variously modified within the scope of the
present invention.

[0194]For example, in the above embodiments, the RLSA plasma processing
apparatus 100 is used in the first nitriding process (step S1). However,
in the first nitriding process, it is also possible to use another plasma
processing apparatus, e.g., a remote plasma processing apparatus, an ICP
plasma processing apparatus, an ECR plasma processing apparatus, a
surface reflected wave plasma processing apparatus, a CCP plasma
processing apparatus, a magnetron plasma processing apparatus or the
like, or a plasma processing apparatus having a plate of which
configuration is the same as that of the plate 60.

INDUSTRIAL APPLICABILITY

[0195]The present invention can be appropriately used to form a silicon
nitride film by nitriding silicon in a manufacturing process of various
semiconductor devices.